fulgide

thumb|right|upright|General chemical structure of fulgides in the uncyclized form. In order to cyclize, at least one of the four R groups must be an aryl group. In organic chemistry, a fulgide is any of a class of photochromic compounds consisting of a bismethylene-succinic anhydride core that has an aromatic group as a substituent. The highly conjugated system is a good chromophore. It can undergo reversible photoisomerization induced by ultraviolet light, converting between the E and Z isomers, both of which are typically colorless compounds. Unlike the more-stable Z isomer, the E isomer can also undergo a photochemically-induced electrocyclic reaction, forming a new ring and becoming a distinctly colored product called the C form. It is thus the two-step Z–C isomerization that is the photochromic change starting from the stable uncyclized form. 500px

==History== The first compound of this class was synthesized in 1906 (by , using the Stobbe condensation), with the name based on the Latin word fulgere, meaning "to shine", for the shiny and large variety of colors of the crystal. The photochromic mechanism of fulgide was reported in 1968. It was not until 1981 that derivatives of fulgide, which made thermally stable photoisomerization, was reported. By editing both non-aromatic substituents and aromatic substituent, fulgide derivatives that are high in thermal stability and photostability were synthesized.